Biodetection Based on Fluorescence Quenching and Surface-Enhanced Fluorescence Using Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 214

high sensitivity, these sensing systems are extremely demonstrated
useful for medical diagnostics.
10.2 Theory
The interactions of luorophores with metallic surfaces can cause
increases or decreases in their luorescence. Fluorescence decreases
are due to energy transfer quenching by metals such as Au and Ag,
which can be understood by the damping of the dipole oscillators
by the nearby metal. 27 On the other hand, SEF is responsible for
increased luorescence, mainly because luorophores are coupled to
propagating surface plasmons near metal NPs.
Figure 10.1 Jablonski diagram without (top) and with (bottom) the
effects of near metal surfaces. For distances over 50 Å
the effect of quenching by the metal ( k m ) is expected to be
minimal. Reprinted with permission from Ref. 28.
Figure 10.1 depicts the Jablonski diagrams of a luorophore in the
absence and presence of a metal. 28 The magnitudes of the radiative
rate (Γ) and the sum of the nonradiative decay rates ( k nr ) govern
the quantum yield ( Q s ) and lifetime ( τ 0 ) of a luorophore. First, we
consider how Γ affects Q s and τ 0 of a luorophore in the absence of
a metal surface. The Q s of the luorophore in the absence of other
quenching interactions is given by